Fine particles having a diameter of from several nanometers to about 1 micrometer have been recently applied in various fields and attracted attention. The above-described fine particles include, for example, porous silica particles and zeolite particles to be used for an adsorbent or a catalyst, carbon black, metal oxide particles and inorganic compound particles to be used for a pigment, metal nanoparticles to be used for a conductive material, and silica particles to be used for a reinforcing agent of resin, and thus, material and use of the fine particles are wide-ranging. Moreover, with regard to semiconductor nanoparticles, silica nanoparticles containing a fluorochrome, and so forth, an application as new labeling particles is expected particularly in a field of biotechnology. In addition, silica nanoparticles containing a pigment with high concentration have a high molar extinction coefficient, and thus, an application thereof as further highly sensitive labeling particles is expected.
The above-described labeling particles can be used as a labeling reagent that can be used for detection, quantitative determination, dyeing or the like of a target molecule, by bonding a biomolecule (protein, nucleic acid or the like) having bonding capability with a specific target molecule on the surface of the particles.